1. Field of the Invention:
The present invention relates to a unit for adjusting the feeding rate of a sewing machine.
2. Description of the Prior Art:
A prior art unit for adjusting the feeding rate of a sewing machine will be described with reference to FIGS. 4 and 5.
The feeding rate adjusting unit comprises a body 1 of an arm of the sewing machine. A feeding rate adjusting shaft 2' is attached to a side of the body 1, is composed of a base 2'a, a screw portion 2'b having a diameter less than the diameter of the base 2'a and threaded into the body 1, and a tip end 2'c to which is moved into contact with a cam surface 7a of a feeding cam 7 (described later). A feeding rate adjusting dial 3 is secured by set screw 4 into an end of the base 2'a of the feeding rate adjusting unit 2'. Dial 3 is provided with a plurality of teeth 3a defined on its inner circumferential surface. A stopper 6 is positioned in a stopper receiver 1a defined in the side of the body 1. A compressed spiral spring 5 is housed in a bottom of the stopper receiver 1a and urges the stopper 6 to mesh with one of the teeth 3a. The feeding adjusting cam 7 has one end having a cam surface 7a provided with a normal feeding control surface and a reverse feeding control surface. The cam 7 has a central portion swingably supported by a cam shaft 8. The other end of cam 7 is connected pivotally to an end of a link 9. Link 9 has an opposite end connected to a feeding adjusting table 10. The feeding adjusting table 10 capable of being turned about a support shaft 11 to be inclined whereby the feeding rate of the sewn cloth is adjusted on the basis of an angle of inclination. A tension spring 12 normally urges the feeding adjusting cam 7 about the cam shaft 8 in the clockwise direction for permitting the tip end surface 2'c of the feeding rate adjusting shaft 2 to be brought into contact with a lower half portion or the normal feeding control surface of the cam surface 7a so that the feeding adjusting table 10 can feed the sewn cloth in the normal feeding direction.
Accordingly, turning the feeding rate adjusting dial 3 varies the distance or amount of moving into or away from the inside of the inner side of the body 1. Locking the feeding adjusting dial 3 at the inner side of the body 1 thereby varies the position of contact of the tip end surface 2c of the feeding rate adjusting shaft with the lower half portion of the cam surface 7a. The inclination angle of the feeding adjusting table 10 connected to the link 9 relative to the shaft 11 is varied to adjust the feeding rate of the sewn cloth in the normal feeding direction.
In case of a backtracking operation, a magnetic solenoid (not shown) is operated by an instruction from a controller (not shown) of the sewing machine whereby first, the shaft 11 is turned at high speed to quickly push the link 9 upward against a tension force of the tension spring 12; secondly, the feeding rate adjusting cam 7 is turned counterclockwise, namely, in the direction of the arrow B; thirdly, the upper half of the cam surface 7a as the reverse feeding control surface strikes heavily and moves into contact with the tip end surface 2'c of the feeding rate adjusting shaft.
However, when the magnetic solenoid is operated to carry out the backtacking operation, the feeding adjusting cam 7 is turned to permit the upper half of the cam surface 7a to momentarily strike the tip end surface 2'c of the feeding rate adjusting shaft. At this point, metallic impact sound is produced which causes operators to become nervous. If the feeding rate adjusting dial 3 is increased in size to improve the working efficiency, a vibrating sound of the feeding adjustment dial 3 is magnified also adversely affecting the operator.